1. Field of the Invention
The present invention relates to a tray used for forming a coating film such as a thick film having a thickness of 20 μm or more on a surface of a substrate such as a glass substrate, a semiconductor wafer, and the like.
2. Description of the Prior Art
Documents 1–4 disclose trays in which a recessed portion is formed to accommodate a substrate such as a glass substrate, a semiconductor wafer, and the like.
Document 1 discloses a tray which is used for forming a film on a surface of a semiconductor wafer by epitaxial growth and has a recessed portion of a greater depth than that of the semiconductor wafer in the central portion thereof.
Document 2 discloses a structure in which a stage for attracting and holding a semiconductor wafer has concentric attracting grooves on the surface thereof, attracting holes are provided in each attracting groove, and these holes are connected to an attracting passage which is bored in the stage. This structure is used at the time of inspecting a circuit and the like formed on a surface of a semiconductor wafer.
Document 3 discloses a tray which is used for forming a film on a surface of a semiconductor wafer by epitaxial growth also. This tray has a recessed portion in the central portion thereof to accommodate a semiconductor wafer, and this tray is mainly made of silicon carbide.
Document 4 discloses a tray for transferring a substrate. This tray has a recessed portion to accommodate a substrate, and an insulative material having flexibility is provided in the recessed portion.                Document 1: Japanese Patent 3336897        Document 2: Japanese Patent Application Publication 2002-289675        Document 3: Japanese Patent Application Publication 2002-313888        Document 4: Japanese Patent Application Publication 2002-313891        
Recently, trials of forming a thick film on a surface of a substrate have been performed. For example, it is necessary to form a resist film having a thickness of around 20 μm so as to form a protruding electrode, which is referred to as a bump, having a height of around 20 μm on a surface of an IC pattern by applying integrated circuit forming technology.
In addition, wire bonding, which has conventionally been used for mounting an IC chip on a substrate, requires labor and time because it is necessary to connect metal wires one by one in wire bonding. Thus, instead of wire bonding, there is another way, in which a plurality of metal posts are provided on a chip, and the chip is mounted on a substrate via the posts. Since the metal posts have a height of around 100 μm, it is necessary to form a resist film having a thickness of around 100 μm so as to form metal posts by applying integrated circuit forming technology.
However, if a conventional tray is used in a coating process for forming such a thick film, it is impossible to solve the following problems which are unique to the coating process.
In a case where the tray of Document 1 or 3 is used in the coating process, a coating liquid which enters between the substrate and the recessed portion of the tray passes a narrow gap between the reverse surface of the substrate and the surface of the recessed portion by capillary action and reaches the whole reverse surface of the substrate (See FIG. 5). This coating liquid becomes particles after drying, and the particles undesirably attach to the surface of the substrate.
In a case where holes are provided as mentioned in Document 2, a coating liquid which reaches the reverse surface enters the holes and prevents the holes from functioning. In this regard, since the plural holes are connected to the single attracting passage in Document 2, once a coating liquid enters the attracting passage, attraction from all holes is interfered with.
In a case where a single hole is provided in the center of the recessed portion as mentioned in Document 4, the reliability of attraction is inferior to the case of Document 2.
Also, if a nozzle is used for supplying a coating liquid to a substrate, there is a tendency that the concentration of the coating liquid is too dense at first. Thus, conventionally, pre-dispensing has been conducted in advance of applying a coating to the substrate. However, if the distance between the pre-dispensing area and the applying area is great, the tip end of the nozzle dries and the effect of the pre-dispensing is deteriorated. Conventional trays cannot solve this problem.